I'm wearing beat up Supergas and a stained mens sweater right now, but beneath that, there's a secret beast inside of me. An absurdly "basic," girly beast who eats Brussels sprouts at Sunday brunches and who will gladly cough up more than $30 for an exercise class (as long as it's, like, totes amazing). The latter's exactly what I did when modelFIT—a new gym from celebrity trainer Justin Gelband—opened so close to my New York City apartment I couldn't resist trying its $40 group classes.

I thought modelFIT's offerings would be intense, because Gelband is famous for training Victoria's Secret Angels, and we all know they work out HARD. (Some of my colleagues have even seen it firsthand.) But when I started taking classes there, I found many of them were way, way easier than the Barry's Bootcamp and SoulCycle sessions I was used to. I was confused. Do the Karlie Klosses and Candice Swanepoels of the world only have to work out like this to look like THAT? I mean, obviously they've largely got the body that's so often strived for in women's exercise classes— "long and lean," the holy grail—due to genetics. But they're also ridiculously toned, so this stuff must work somehow, right? After my first session, I wasn't so sure.

During my first "Sculpt" class in modelFIT's sleek, glossy studio, I was told to "slow downnnnn" with my movements so often it felt like my first driving lesson as a 16-year-old. And it was off-putting: I was so indoctrinated with the idea of high intensity interval training that I just wanted to GO GO GO at everything—at all those leg raises, crunches, and arm lifts that make up the bulk of the class. The friend I brought felt the same way: We were both used to measuring the success/failure of a class on a sweat barometer, and her fresh blowout was barely damp afterward. At dinner, over Shiraz and kale salads (I'm basic, remember?), we talked about how we weren't sure it was gonna be that effective.

Then the day two soreness hit, and it cut deeeeeep. I returned to modelFIT with a new outlook, and asked its co-founders, Vanessa Packer and Justin Gelband, how exactly my body generated so little sweat but so, so much soreness. Packer laughed, because apparently I had just figured out the modelFIT "philosophy." It's all about doing those "small movements at a slow pace," she said, for "mindful exercise that tones and strengthens your entire body." And sneakily, at that. I mean, I know less cardio-heavy classes are nothing new, that there are women that love barre, ballet, and Pilates. But could that sort of workout, which modelFIT seemed to be mostly, deliver the sort of definition and toning seen on the Victoria's Secret runway? Could it really be that effective?

Over the next few weeks, I switched my four to five times per week SoulCycle habit to a three to four times per week modelFIT one. I was in good shape already, and yet I still leaned out from switching off spinning and over to modelFIT classes (even though I was working out less times per week!) for two reasons:

Part of it was the mental effect, I realize. When I thought I was doing a lighter, possible-to-do-while-hungover workout, not a "I want to die every minute even though I'm fully hydrated and healthy" cardio class, I didn't feel quite as tempted to reward myself by overeating the rest of the day. I ate better, but not consciously. It just sort of happened when I no longer felt like I was Angelina Jolie training for Tomb Raider.

But the bigger part, I'm sure, was the method. I could actually start to see a faint shadow in that column of my torso around my abs. My waist was being "whittled," like Karlie. Gelband explains it as a direct benefit of the slow pace of his classes, saying that focusing on proper form lets women really "get the motions and the movements down and feel the small muscles working," exercising those "muscles as the workout intends."

While concentrating on getting all that right, Packer adds, the "slow, controlled, focused moments really get your heart racing" without you even knowing. It's sneaky cardio, and it's pretty brilliant. That's the genius part: modelFIT will give a girl a good workout without even fully realizing how good it is—and without ruining her blowout. What could a basic babe like me, Karlie Kloss, or Karlie's new BFF Taylor Swift—who was seen leaving the gym last week—appreciate more than that?

Maybe more modelFIT studios nationwide, I suppose. (In the meantime, those outside of NYC can always watch Gelband's method from home via YouTube.)